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50 µs 555-Timer-Monostable for EEPROM burning

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Volvagia

New Member
I want to burn an EEPROM (29EE010) and need for this a ~+5V (High) peak for between 0.5 and 100 microseconds. It is a bit embarrassing, that I fail on such an easy circuit, but I have no idea what I doing wrong. The new data are not written, and all other parts seems to work. The Monostable should peak on each button press for ~50 µs. (1.1 * C3 * R3 = 1.1 * 0.47 * 100 = 51.7)

Thank you

monostable.png
 

audioguru

Well-Known Member
Most Helpful Member
The value of 100 ohms for your timing resistor is much too low. The datasheet shows 1k to 10M. If you use 10k then the capacitor can be a smaller and less expensive 4.7nF. Your 100 ohms might have burned out the pin 7 transistor.
Your 2.7k and 0.1μF parts for the trigger pulse make the pulse much too long. The datasheet shows 10k and 0.001μF.
 

gophert

Well-Known Member
Most Helpful Member
I want to burn an EEPROM (29EE010) and need for this a ~+5V (High) peak for between 0.5 and 100 microseconds. It is a bit embarrassing, that I fail on such an easy circuit, but I have no idea what I doing wrong. The new data are not written, and all other parts seems to work. The Monostable should peak on each button press for ~50 µs. (1.1 * C3 * R3 = 1.1 * 0.47 * 100 = 51.7)

Thank you

View attachment 112291
Do you have a "debounce" circuit for the button - if not, it could vibrate on releas and retrigger the 555.
 
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AnalogKid

Well-Known Member
Most Helpful Member
A 555 is not the best part for this for several reasons.

A CMOS LMC555 will have an output voltge that is closer to the 5 V output requirement.

A 555 is not a true monostable because it does not have any positive feedback. The trigger input R-C time constant is 27 us, dangerously close to the 50 us output period. Also, it is too short to debounce SW3. After the 50 us output pulse id sone, switch bounce could cause another output pulse or several pulses in a quick burst.

How much output current do you need during the 5 V pulse period?

ak
 

Volvagia

New Member
Thank you very much. I have updated the circuit as audioguru recommended, but it still won't work. I think I need to add a capacitor to debounce the button like on the second image, but I am not sure if it is the right way. Luckily the 555 works after the high currency still like expected. The ROM seems not to drive currency from the WE, it needs only the voltage.

Edit: Replaced second image, was wrong.
 

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