please tell if i have something wrong

[audioguru]

That circuit uses 8 transistors and the motor gets a minimum of 8V.
My circuit uses only 6 transistors and the motor gets a minimum of 11V.

 

[ericgibbs]

hi Watzman,
I would strongly recommend that you use 'audioguru's version of the circuit, you will get the results you are expecting.

 

[watzmann]

excuse me 'audioguru's i didn't notice that your circuit is actually so simple .

i'll build it today.

bytheway......what about the L293D ?

do you know any disadvantages for this IC?

 

[Hero999]

Yes, it's very low current, only 600mA, 1.2A peak - it'll only drive the smallest of motors.

 

[audioguru]

what about the L293D ?
do you know any disadvantages for this IC?

Look at its datasheet!
1) Its max continuous current is only 600mA so it can drive only very small motors.
2) With a 600mA motor its total max saturation voltage loss is 3.6V.
3) Its total max supply current is 84mA when it is doing nothing.

 

[watzmann]

so it's just a hobby ic.

do you use an electronic simulation software for testing your schematics , audioguru ?

 

[audioguru]

do you use an electronic simulation software for testing your schematics , audioguru ?

All my circuit designs work fine so I have never simulated them.
Hero simulated my FM transistor to show how to make it more powerful.

I use Sw-CAD III sim program from Linear Technology (it is free) to simulate other people's horrible designs to show how bad they are.

Here is the mic preamp from somebody's horrible FM transmitter and my fix for it:

 

[watzmann]

i have built the H-Bridge PCB and i'll assemble it's components today and try it ....hope it will work fine

 

[watzmann]

i tested the new H-Bridge but it doen't work well , i noticed that one of the TIP 41 is going too hot .....and the motor work even without any signal.....i'll post you my schematic and tell me why that had happened?

 

[audioguru]

i tested the new H-Bridge but it doen't work well , i noticed that one of the TIP 41 is going too hot .....and the motor work even without any signal.....i'll post you my schematic and tell me why that had happened?

Maybe your motor draws much more than 3A. Measure its resistance. If it is 4 ohms then its max current from 12V is 3A.

Only one signal can be high at a time. If both are high then there will be smoke.

When a signal is at ground then the BC337 is turned off and it turns off the associated TIP41 and TIP42. Therefore when both signals are low then none of the transistors are turned on.

 

[watzmann]

i fixed the transitstors with the right way i'm sure.......but i'm afriad that happned becuse of the LED i added

 

[audioguru]

i fixed the transitstors with the right way i'm sure.......but i'm afriad that happned becuse of the LED i added

Your LED is connected to the supply voltage. It doesn't affect the transistors.
1) Does the input signal go to 0V when it is turned off?
2) Does the input signal go up to near +5V when it is turned on?
3) What are the resistor values?
4) Does the motor draw only 3A max? Measure its resistance.

The circuit might need protection diodes across the power transistors.

 

[watzmann]

i'll answer two of your questions now:

1- motor current consumption is so low.less than o.4 A
2- resistor values are , 1 Kohm and 33 ohm and 150 ohm.....is that correct

 

[audioguru]

A motor that uses 0.4A without a load draws 4A or more when it starts, when it is loaded or when it is stalled.

 

[watzmann]

anyway i'll prepare aother PCB may be that is the reason and i'll try a very small motor.

something else i need to ask about :

in the LM338 datasheet i have found an application for 12 volt battery charger using this regulator and ic lm301A .... what is the advantages of using this circuit ?

i mean what is the differance between this circuit and the simple one which use just the lm338 and a potentimeter.

 

[blueroomelectronics]

An L292 would do the trick.
Drive it directly from the PIC. Can even use the PWM on the 16F877
**broken link removed**

 

[watzmann]

ya i know this chip but it has at least one disadvantage with my application..it's MIN supply voltage is 18 and i'm going to use just one battery on my robot with 12 Volts.

i'm trying to make a new H-Bridge with Auduioguru idea ...i know it's correct design...so it will work i'm sure

 

[watzmann]

i'm using in this h-bridge a new compontents except the two TIP 41 transistor ...... can i test this TIP 41 with the AVO meter like the usual transitor?

 

[audioguru]

You said that the motor runs without any signal. Then both inputs should be 0V. If the motor runs then a BC337 is conducting when it shouldn't.