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Delay circuit for IR2110 base H Bridge (DC motor)

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usmanyousaf

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Hi,

i am designing an H Bridge to drive DC motors. i intend to use only PWM to control speed and direction of the motor. i need to do it at high frequency atleast more than 20kHZ so that the switching noise is not audible. I want to make a delay circuit, since im controlling with only PWM i cannot use microcontroller to incorporate the delay. the MOSFETs i plan to use are IRF540.

thankyou.
 

Tahmid

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Hi,

i am designing an H Bridge to drive DC motors. i intend to use only PWM to control speed and direction of the motor. i need to do it at high frequency atleast more than 20kHZ so that the switching noise is not audible. I want to make a delay circuit, since im controlling with only PWM i cannot use microcontroller to incorporate the delay. the MOSFETs i plan to use are IRF540.

thankyou.

What delay are you talking about? Deadtime(deadband delay)? Or are you talking of some other delay?

Which PWM controller is being used? Most PWM controllers (that I know of) have deadtime circuitry built into them. You usually just need an extra resistor.
 
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usmanyousaf

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thanks for you reply...

I will be using builtin PWM generator of Atmega16/162. and yes im talking about deadband delay. i want to use same signal for HIN and LIN of IR2110 with a not gate and dealy circuit between them. hope i make my question clear...

- - - Updated - - -

thanks for you reply...

I will be using builtin PWM generator of Atmega16/162. and yes im talking about deadband delay. i want to use same signal for HIN and LIN of IR2110 with a not gate and dealy circuit between them. hope i make my question clear...

- - - Updated - - -

thanks for you reply...

I will be using builtin PWM generator of Atmega16/162. and yes im talking about deadband delay. i want to use same signal for HIN and LIN of IR2110 with a not gate and dealy circuit between them. hope i make my question clear...
 

Tahmid

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Why don't you implement the delay in software? Instead of using the same signal, you can generate the second signal using the ATMEGA and add the deadband delay too. This will reduce external parts count as well.

If you can use other drivers, there are drivers available which allow you to add and adjust the deadtime.
 

usmanyousaf

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can you suggest any driver which has deadband delay builtin for frequencies above 20kHz.

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well aim of my project is to do it with hardware, but how can i do it with software..?? =)
 

Tahmid

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IR21834, IR21844.

If you use IR21844, you get another advantage. It is a half-bridge driver, which means that it has one input only. The inverting that you were talking about need not be done since the low-side MOSFET will be driven with a '0' (low) input anyways.

Other drivers (such as IR2183, IR2184) have internal fixed deadtime. IR2183 and IR2184 have fixed 500ns deadtime.

Hope this helps.
Tahmid.
 

usmanyousaf

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thanks Tahmid, what should be the dead time for 20kHz. is it just inverse of frequency or some rocket science..??
 

Tahmid

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Inverse of frequency is the time period.

Deadtime is the time for which the MOSFETs are all kept off to prevent cross-conduction and shoot-through.

1us should be more than enough.

Hope this helps.
Tahmid.
 

picgak

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usmanyousaf if you are using Atmega you can implement deadtime while writing software itself
 

goodboy_pl

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usmanyousaf,
referring to page 19 of the pdf document, you can see the dead time circuit. it consists of a Resistor, a capacitor and a diode. A comparator is used to convert analog slow signals to sharp digital transitions.
How it works?
1) In 0 to 1 transition at input, the output of comparator will have a delay (typically 100ns to 1us) which is determined by RxC time constant and the diode is off.
2) In 1 to 0 transition at input, the output of comparator will have no delay (theoretically of course!) because the diode is on in this mode.
In this way the MOSFET turn-on signal is delayed but the turn-off is almost immediate. this prevents shoot-through in bridge configurations.
Though it is possible to implement dead time in microcontrollers, discrete implementations is robust and fail safe since it is hard-wired in nature.
The circuit is designed in various forms but the concept is the same even if integrated in driver ICs. for example the comparator could be replaced by a schmitt trigger.
 
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