Hello everyone,
I am new to electronics and I have been searching for a 20khz pwm circuit with soft start. This will be used for a 12v, 30 amp automotive radiator fan. The soft start is needed for the 80am draw on initial start up. There are 12v relays involved to handle the input from various conditions such as Low, High, AC etc. All that has been worked out.
I have seen both direct dc soft start and 555 astable pwm circuits but never a soft start 555 astable pwm (see attachments- the DC soft-start says 24v but I only need it for 12v so I assume some values will have to be changed). I am going to use N-Channel mosfets in parallel and have also been looking at gate drivers to handle them.
I also have been souring the web for a simple chip that doesn't require programing that can accomplish everything, other than the gate driving. I think I have found some ic's but they become very complicated and seem to be geared for brushless motors.
I need to have two speeds, which to my understanding will require two 555 chips. I have found 555 calculators on the web which when using the correct resistors and capacitors will give me duty cycles around 53% for the slow and 98% for the high speed at 25khz.
I have run a simple 555pwm in Mouser's Milti-Sim Blue software and it seems to work ok except for what looks like an occasional hick-up on the oscilloscope.
I have taken this as far as I can go and really need some professional insight. If anyone can make some suggestions I would appreciate it.
Thanks.