SURF PI 555 QUESTION

[Teleno]

Hi Qiaozhi

is there a way around this problem ????

By changing the voltage of the 555 to 15V you've also set the gate-sorce voltage that dives the MOSFET to 15V. This decreases the on-resistance of the MOSFET, which in turn increases the current. If the MOSFET current is not limited (for example, using a source resistor) then its current increases with the on-time time as a ramp, which can be catastrophic. Limiting the MOSFET current is essential if you don't dig smoke.

By th way, the 555 can also be configured as a negative voltage generator instead of the ICL7660 or the LT1054.

[daverave]

Hi Qiaozhi

is there a way around this problem ????

[Qiaozhi]

im using the surf pi so the ICL 7660 is regulated at 5v...but its the 555 which is the problem as i regulated it at 15v and higher voltage to the coil then as i said the current consumption went up big time and mosfet was burning hot and the ICL 7660 and 555 were destroyed and one of the clipping diodes went low resistance...it was like the mosfet was not being switched off correctly.

In that case I think I can see the problem.
The MOSFET gets turned off when the 555 output goes high, but you've restricted the voltage supply to 15V. Since the MOSFET is connected to 18V, this leaves a 3V difference between the gate and source of the MOSFET. In other words, the MOSFET is permanently turned on. No wonder it got hot!

[daverave]

im using the surf pi so the ICL 7660 is regulated at 5v...but its the 555 which is the problem as i regulated it at 15v and higher voltage to the coil then as i said the current consumption went up big time and mosfet was burning hot and the ICL 7660 and 555 were destroyed and one of the clipping diodes went low resistance...it was like the mosfet was not being switched off correctly.

[Qiaozhi]

Supply voltage of 7660 is limited to under 11V. LT1054 is the same thing, but runs up to about 15V.

ICL7660 has an operating voltage range of +1.5V to 10.0V, and ICL7660A has a range of 1.5V to 12.0V.
The absolute maximum voltages are 10.5V and 13.0V respectively.
These device also have a tendency to curl up and die if these limits are exceeded, which is why the MPP uses an LT1054.

The LT1054L has an operating voltage range of 3.5V to 7.0V, and the LT1054 has a range of 3.5V to 15.0V.
Absolute maximum values in this case are 7.0V and 16.0V respectively.

[Davor]

Supply voltage of 7660 is limited to under 11V. LT1054 is the same thing, but runs up to about 15V.

[WM6]

Check pulse length (by changing 555 supply voltage you change its pulse parameters too).

[daverave]

I want to use a 15v regulator to the 555 oscillator chip and 18v to the coil but when i tried this the coil drive was badly affected and mosfet draw very high current and the 7660 and 555 chips were damaged...what can i do to get around this problem cause i need to regulate the voltage to the 555 chip ???????