Mobile charger

[thecritic]

I want to design a simple mobile battery charger, to be installed in my electric bicycle. The bicycle operates at around 50 Volts DC. I could use a LM7805 voltage regulator, but I don't think it can handle 50 Volts. Also, I don't want to waste much power.
Any suggestion please!

( I guess providing a simple constant 5V is enough to charge my mobile battery)

 

[blueroomelectronics]

National semiconductor makes a few HV rated switchmode regulators.

 

[thecritic]

And don' the switchmode regulators waste the energy?
I have an idea, but I am totoall unsure whether it is madly flawed or not.
The idea is this:
1.Design a High frequency (say 1Khz) 555 timer circuit with just 10% duty cycle
2. use the frequency to drive a transistor that operates on the 50 Volts. Since the output of the transistor is 50V with 10% duty cycle, use it to charge a capacitor. The final voltage across the capacitor (if it is constantly being discharged to charge the mobile) will be around 5 Volts.
3. Use the voltage across the capacitor to charge the mobile.

 

[blueroomelectronics]

It's linear regulators that are inefficient. Google Simple Switchers such as the LM2575 (look for the HV versions)

 

[MikeMl]

duplicate post, please ignore.

 

[MikeMl]

...
I have an idea, but I am totoall unsure whether it is madly flawed or not.
The idea is this:..

You have just described a switch-mode converter, except you left out a couple of essential items. First, when the 555 switch is closed, you need something to limit the charging current to the capacitor. Otherwise the instantaneous charging current would be very large. If you insert a resistor, you are wasting lots of power. Usually, an inductor is what is inserted. The inductor prevents the current surge by letting the current build up slowly. This limits the charging current to the capacitor, but it also stores energy in the inductor, which can be recovered, and used to power the load. However, it takes one more component to steer the inductor current to the load; a Schottky diode. Now you have a complete Buck Converter.

btw: Buck converters typically run at 20kHz to ~2MHz and are ~85% efficient.

 

[Hero999]

A simple SMPS can be built using a couple of transistors. If increase the resistor values and use transistors rated to 60V, you can easily run this off a 50V battery.
2-transistor Black Regulator

A push-pull or forward converter would be better than a buck for 50V in and 5V out but it's not worth the added complexity for such a small amount of power.

 

[thecritic]

A simple SMPS can be built using a couple of transistors. If increase the resistor values and use transistors rated to 60V, you can easily run this off a 50V battery.
2-transistor Black Regulator

A push-pull or forward converter would be better than a buck for 50V in and 5V out but it's not worth the added complexity for such a small amount of power.

I didn't see any frequency source in the black regulator, I guess it is automatically generated by the LC circuit.

Should I follow all the recommendation the site provides for using High Voltage, Especially, should I use darlington pair?

Which easy to find transistor would you suggest for 50Volts?

 

[sahu]

A simple SMPS can be built using a couple of transistors. If increase the resistor values and use transistors rated to 60V, you can easily run this off a 50V battery.
2-transistor Black Regulator

.

i want use it 220v dc i\p & 5vdc o\p.
what' calculation of resistor values.