# Datasheet Question

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#### Waldo Pulanco

##### New Member
i was wondering on how to read a datasheet for transistor i mean i mean if i want to bias or operate the transistor how to prevent it from damaging,
i have read the data sheet and i want to know some basic info example

Code:
collector-base voltage = 55V condition open emitter

Collector-emitter voltage = 55V condition RBE = 10 Ohms

Collector-emitter voltage = 30V condition Open Base

Emitter-base voltage = 3.5V condition open collector

Collector current(DC) = 0.4A

collector current peak value = 0.4A

total power dissipation = 3.5W condition up to Tmb = 25 °C

storage temperature = +200 °C

junction temperature = 200 °C

Power Output  = 1W

Please can you explain it!! i want to know some basic information in datasheet!!

#### audioguru

##### Well-Known Member
The limits are all there and most of the conditions are there:
1) Maximum allowed voltages. Do not exceed them.
2) Maximum allowed currents. Do not exceed them.
3) Maximum power dissipation with an impossible "perfect" heatsink.
4) Maximum allowed temperature.
5) The maximum allowed power output does not make sense because it has no conditions.

Do you have a question about any of these limits?

#### Waldo Pulanco

##### New Member
The limits are all there and most of the conditions are there:
1) Maximum allowed voltages. Do not exceed them.
2) Maximum allowed currents. Do not exceed them.
3) Maximum power dissipation with an impossible "perfect" heatsink.
4) Maximum allowed temperature.
5) The maximum allowed power output does not make sense because it has no conditions.

Do you have a question about any of these limits?

thanks sir for response!
example total power dissipation = 3.5W can i have use 2watts for operation or it can destroy the transistor?

#### audioguru

##### Well-Known Member
example total power dissipation = 3.5W can i have use 2watts for operation or it can destroy the transistor?
The transistor will be at its maximum allowed internal temperature (200 degrees C) with 3.5W of dissipation if you cool its MB (mounting base) to 25 degrees C somehow.
But the mounting base will heat up even if it has a huge heatsink and a fan so the maximum allowed dissipation will be less than 3.5W depending on the ambient temperature and the efficiency (surface area and air flow) of the heatsink.

You can calculate the thermal resistance required for the heatsink then find a suitable heatsink that has that thermal resistance in a catalog.

#### Waldo Pulanco

##### New Member
The transistor will be at its maximum allowed internal temperature (200 degrees C) with 3.5W of dissipation if you cool its MB (mounting base) to 25 degrees C somehow.
But the mounting base will heat up even if it has a huge heatsink and a fan so the maximum allowed dissipation will be less than 3.5W depending on the ambient temperature and the efficiency (surface area and air flow) of the heatsink.

You can calculate the thermal resistance required for the heatsink then find a suitable heatsink that has that thermal resistance in a catalog.

thanks!! now i understand!! i think the 2 watts operation with heat sink is enough and not destroy the transistor!!

#### ronsimpson

##### Well-Known Member
The temperature is simple. Keep your finger on the transistor. If you can't then you cave temperature problems.

#### rumpfy

##### Active Member
From the information you give, the thermal resistance of the transistor is 37 degree C per watt from the junction to the mounting base. You say the maximum junction temperature is 200 degree C but I think this is a 'storage temperature'. It is more likely that the operating junction temperature is around 150 degree C. The 37 degree C per watt is based on a maximum junction temp of 150 deg C.
If you want to run the transistor with a 2 watt dissipation in an ambient air temperature of 40 degree C, then the thermal resistance from junction to ambient will be 150-40=110 degree per 2 watt which works out to 55 degree C per watt. The thermal resistance of the device is 37 deg C /watt so you need to have a maximum of 55-37 = 18 degree C per watt as the thermal resistance of the heat sink. This is a small heatsink as heat sinks go.

#### Waldo Pulanco

##### New Member
From the information you give, the thermal resistance of the transistor is 37 degree C per watt from the junction to the mounting base. You say the maximum junction temperature is 200 degree C but I think this is a 'storage temperature'. It is more likely that the operating junction temperature is around 150 degree C. The 37 degree C per watt is based on a maximum junction temp of 150 deg C.
If you want to run the transistor with a 2 watt dissipation in an ambient air temperature of 40 degree C, then the thermal resistance from junction to ambient will be 150-40=110 degree per 2 watt which works out to 55 degree C per watt. The thermal resistance of the device is 37 deg C /watt so you need to have a maximum of 55-37 = 18 degree C per watt as the thermal resistance of the heat sink. This is a small heatsink as heat sinks go.

Idont understand!! please tell me what is storage temperature, junction temperature and ambient air temperature. where did you get 37 deg C per watt? please tell me i want to know more about datasheet of transistor!!

thanks!!

#### audioguru

##### Well-Known Member
Idont understand!! please tell me what is storage temperature, junction temperature and ambient air temperature.
You said that the maximum allowed storage temperature is 200 degrees C. You said that the maximum allowed junction (inside the transistor) temperature is also 200 degrees C. The ambient air is the air around the product which might be 25 degrees C inside a room in a home or 40 degrees C inside a closed cabinet.

where did you get 37 deg C per watt?
If the maximum allowed junction temperature is 150 degrees C and the ambient temperature is 40 degrees C then the temperature from the junction to the ambient is 150 - 40= 110 degrees C. But the maximum allowed dissipation when its mounting base is 25 degrees C is 3.5W. Then 3.5W is allowed to heat the junction (150 degrees - 25 degrees=) 125 degrees. So the thermal resistance from the junction to the mounting base is 125/3.5= 36 degrees C per Watt.

You want 2W so the temperature is allowed to rise 2 x 36= 72 degrees C from 40 degrees to 72 + 40= 112 degrees C.
Then the heatsink must cool the mounting base 150 degrees - 112 degrees per 2W which is a thermal resistance of (150 - 112)/2= 19 degrees C per Watt.

Use a larger heatsink because the transistor will last longer if it never reaches its maximum allowed temperature.
This heatsink will be fine:

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